The closest prior art based on the fact that they all appear to disclose genetically modified strains of S. cerevisiae having the GDH1 gene at least partially deleted appears to the following:
U.S. Pat. No. 7,018,829 requires only a reduced enzyme activity of a natively present NADPH-dependent glutamate dehydrogenase (as compared to the native level of activity), which, according to a preferred feature, may be achieved by deletion of at least part of at least one native regulatory sequence associated with the native nucleic acid coding for glutamate dehydrogenase or, alternatively, by operably linking the coding sequence of the native glutamate dehydrogenase to a regulatory sequence not natively associated therewith.
A1 Geotkjaer T. et al., Metab. Eng. 2005: 7(5-6), 437-444 (“Comparative metabolic network analysis of two xylose fermenting recombinant Saccharomyces cerevisiae strains”).
A2 Noreira dos Santos M. et al., FEMS Yeast Res. 2003: 4(1), 59-68 (“Aerobic physiology of redox engineered Saccharomyces cerevisiae strains modified in the ammonium assimilation for increased NADPH availability”).
A3 Roca C. et al., Appl. Environ. Microbiol. 2003: 69(8), 4732-6 (“Metabolic engineering of ammonium assimilation in xylose-fermenting Saccharomyces cerevisiae improves ethanol production”).
A4 Nissen T. L. et al., Metab. Eng. 2000: 2(1), 69-77 (“Optimization of ethanol production in Saccharomyces cerevisiae by metabolic engineering of the ammonium assimilation”) discloses a genetically manipulated S. cerevisiae strain having the GDH1 gene deleted and two other genes in the glutamate synthetic pathway overexpressed. It further seems that all the strains disclosed by the above documents (which all appear to derive from one research group) are characterized by an increased ethanol and reduced glycerol production, which effects seem to be attributed, at least in part, to the deletion of GDH1 gene.
All the genetically modified S. cerevisiae strains disclosed by papers A1 through A4 and U.S. Pat. No. 7,018,829 seem to include genetic modifications additional to the deletion of GDH1 gene (those disclosed in papers A1 and A3, for example, are xylose-fermenting strains comprising heterologous genes making possible xylose to ethanol conversion, a capacity native strains of S. cerevisiae lack). They also all involve laboratory rather than industrial strains of yeast. In passing it should be noted that laboratory strains of yeast are mainly haploid with a single complement of genetic material whereas industrial yeasts are very often polyploid having more than one complement of genetic material which makes them difficult and unpredictable to work with.
It is, therefore, still desirable simply to provide an improved industrial strain of Saccharomyces cerevisiae capable of decreased glycerol production, increased ethanol production and increased tolerance to high concentrations of ethanol.